A tape drive such as an LTO (Linear Tape Open) tape drive writes data to a tape sequentially in the longitudinal direction of the tape medium. The tape drive uses the appended writing format to write and update data, and data becomes unreadable when data is changed on the tape. The first half of data written to the tape is unneeded data, updated data is appended to the second half as needed data, and new data cannot be written to the areas in which unneeded data is stored. The unneeded data remains on the tape cartridge, and the entire capacity of the medium cannot be effectively used.
The Linear Tape File System (LTFS) is a file system that can handle data on a tape using a file format. LTFS can use the same tape drive file system as a fifth-generation Linear Tape Open (LTO5) tape drive and the fourth-generation IBM Enterprise TS1140 tape drive. When files are edited in an LTO tape drive using LTFS, the reading and updating characteristics described above pose a significant challenge.
Even when files written to LTO using LTFS are deleted, data from the deleted files remains on the tape. When the content of files is not deleted but updated, the updated data is appended to the end of the tape, and the data prior to the update remains on the tape. The areas in which unneeded data is written cannot be reused for the reasons described above. Therefore, the capacity of the tape may not be sufficient to accommodate frequently updated files even when the actual size of the files has not increased.
Reclamation can be performed to reuse data storage area on a tape when the amount of unneeded data on the tape has increased. In the reclamation method of the prior art, the needed data is copied from one tape to another. Two drives are needed during the copying process. Two tapes are also required: a source tape and a destination tape. A method is currently being considered in which tape data is transferred to a hard disk drive (HDD) and then written directly to a tape. The tape capacity in LTO5 is 1.5 TB when data compression is not used. Therefore, an HDD requires a work space of 750 GB just to handle the unneeded data taking up half the capacity.
A tape drive is described in PCT Publication No. 2010-522914 in which two cartridges are used in the reclamation process: a source medium and a destination medium for copying data.